Air valve type carburetor and method of construction

ABSTRACT

In an air valve-type carburetor in which a suction piston is mounted in a suction chamber, fixed to the main body of the carburetor, in such a manner that it will be slidingly projected from or retracted into said suction chamber under the influence of the suction pressure in the air intake passage of the carburetor, and a jet needle is fixed to said suction piston, while a fuel nozzle is provided in the main body of the carburetor, and the fuel metering area is varied by said jet needle moved into and out of said nozzle, a method of producing a positioning pin for maintaining said jet needle and said nozzle in a fixed relative position which is determined by the main body of the carburetor and the suction chamber, said method comprising boring holes through the main body of the carburetor and suction chamber in communication with each other and pouring a molten resin or the like into said holes to form a positioning pin after the relative position of said carburetor main body and suction chamber has been adjusted.

llite States ate t 1 1 ,7

awai et al. Jan. 8, 1974 AIR VALVE TYPE CARBURETOR AND METHOD or CONSTRUCTION [57] ABSTRACT [75] Inventors: lsamu Kawai, Katsuta; Tadao Uchida, Hitachi; Kenji Ishima, Katsuta, all of Japan Assignee: Hitachi Ltd., Tokyo, Japan Filed: July 7, 1972 Appl. No.: 269,732

Primary ExaminerTim R. Miles Attorney-Paul M. Craig, Jr. et al.

In an air valve-type carburetor in which a suction piston is mounted in a suction chamber, fixed to the main body of the carburetor, in such a manner that it will be slidingly projected from or retracted into said suction chamber under the influence of the suction pres sure in the air intake passage of the carburetor, and a jet needle is fixed to said suction piston, while a fuel nozzle is provided in the main body of the carburetor, and the fuel metering area is varied by said jet needle moved into and out of said nozzle, 2. method of producing a positioning pin for maintaining said jet needle and said nozzle in a fixed relative position which is determined by the main body of the carburetor and the suction chamber, said method comprising boring holes through the main body of the carburetor and suction chamber in communication with each other and pouring a molten resin or the like into said holes to form a positioning pin after the relative position of said carburetor main body and suction chamber has been adjusted.

PAIENIEDJAN 81924 3784.173

FIG. I

mnnnd AIR VALVE TYPE CARBURETOR AND METHOD OF CONSTRUCTION This invention relates to an air valve-type carburetor in which a suction piston is slidably mounted in a suction chamber fixed to the main body of the carburetor, in such a manner that it will be projected from or retracted into the suction chamber according to .the suction pressure in the air intake passage ofthe carburetor and a jet needle is fixed to said suction piston, while a fuel nozzle is provided in the main body of the carburetor, and the fuel metering area is varied by said jet needle moved into or out of said nozzle.

The most important matter for the uniformity of flow rate of fuel supplied from a carburetor of the type described above to an engine is the centering of the jet needle relative to the nozzle, and various methods have been employed for improving the centering accuracy but none of them is entirely satisfactory. Namely, the fuel flow characteristic of this type of carburetor is that the flow rate of fuel is controlled over the entire operational range of the engine from the idling phase to the highest speed operation phase of the engine, solely by the combination of the nozzle and jet needle. Therefore, the carburetor is required to be highly precise in construction and, by reason of the construction, a relative displacement of the nozzle and jet needle off the centering will result in a variation and an increasing fluctuation of the flow rate. Thus, the carburetor cannot meet the increasing demand for the improvement in uniformity of fuel flow rate under the automobile exhaust gas restriction law which is becoming severer year after year. For improving the accuracy of centering of the jet needle and nozzle, it is the recent trend to regulate the position of the jet needle provided integrally with the suction piston and suction chamber, by moving the jet needle relative to the main body of the carburetor.

Namely, a method has been employed in which the relative position of the nozzle and jet needle is determined with accuracy, by shifting the suction chamber relative to the main body of the carburetor and thereafter the suction chamber is secured to the main body of the carburetor by means of screws. However, this method has the disadvantages that the connection of the suction chamber and the carburetor becomes loosened under vibrations of the automobile and the amount of eccentricity between the nozzle and jet needle increases and that the amount of eccentricity must be adjusted every time the carburetor is assembled subsequent to disassembly. There has been employed another method in which the relative position of the nozzle and jet needle is determined accurately by shifting the suction chamber relative to the carburetor main body and then the carburetor main body and suction chamber are fixed in their positions by means of positioning pins to maintain the nozzle and jet needle in said relative position. These positioning pins are used for the purpose of placing the carburetor main body and the suction chamber always in the fixed relative position in the assembly of these two elements after disassembly.

Metallic pins have been used for such positioning pins, which are fabricated by machining, and pin receiving holes are bored concurrently through the stationary element (carburetor main body) and movable element (boss of the suction chamber). Each pin has stepped portions and the large diameter portion thereof is forced into the hole bored through the stationary element and fixed therein. However, in such a method, a relative displacement of the nozzle and jet needle is inevitable after the adjustment of eccentricity, due to vibration and shocks given to the respective elements at the time of driving the suction chamber positioning pins into the holes subsequent to the adjustment of the amount of eccentricity of the jet needle. On the other hand, if attempt is made to minimize the positional deviation, the efficiency of the positioning pin mounting operation will be impaired.

An object of the present invention is, in an air valvetype carburetor, to maintain the relative position ofthe nozzle and the jet needle by means of positioning pins in such a manner that said relative position may be reproducible.

Another object of the invention is to make accurate mounting of the positioning pins possible and to enable the mounting operation to be achieved simply and quickly.

The feature of the present invention lies in the fact that, in an air valve-type carburetor in which the relative position of the nozzle and the jet needle is adjusted by the relative position of the carburetor main body and the suction chamber, positioning pin-receiving holes are bored through the carburetor main body and the boss of the suction chamber in communication with each other beforehand, and after adjusting the relative position of said carburetor main body and said suction chamber, a material such as a molten resin is poured into said holes to form a positioning pin.

FIG. 1 is a vertical sectional view of the essential portion of an air valve-type carburetor having a positioning pin according to one embodiment of the present invention; and

FIG. 2 is a sectional view showing the details of the positioning pin according to the embodiment of the invention.

For describing an embodiment of the present invention, the construction of an air valve-type carburetor for which the present invention is intended, will be described at first with reference to FIG. 1 of the drawings. In FIG. 1, reference numeral 1 designates a main body of a carburetor to which a suction chamber 2 is fixed as by screws (not shown), and a suction piston 3 is mounted in said suction chamber 2 in such a manner that it is projectable from and retractable into said suction chamber in sliding engagement with the inner surface of the suction chamber 2. Namely, the lower portion of the suction piston 3 moves into and out of an air intake passage 5 according to the size of the suction pressure in said air intake passage, which is acting on the inner bottom surface of the suction piston 3 through a suction hole 4, whereby the sectional area of a Ventri 6 is varied. Concurrently, a jet needle 7 fixed to the suction piston 3 slidably moves into and out of a nozzle 8 provided in the lower portion of the carburetor main body 1, changing the fuel metering area. The nozzle 8 is slidably mounted in a nozzle guide sleeve 9 mounted in the carburetor main body 1, and held in position as by a spring (not shown). In an assembled state of the air valve-type carburetor of the construction described above, it is necessary for the nozzle 8 to be in axial alignment with the jet needle 7 and this is achieved by fabricating the component parts such that the axis of the nozzle guide sleeve 9 will be at right angles to the end face of a boss 2' of the suction chamber 2 or the contacting face of the carburetor main body 1 with the suction chamber 2, because the jet needle 7 is fixed to the suction piston 3 and the sliding direction I thereof is determined by the position of the suction chamber 2, then shifting the suction chamber 2 on the contacting face 10 into a position in which the nozzle 8 will be in axial alignment with the jet needle 7, and securing the suction chamber 2 to the carburetor main body 1 in said position. The suction chamber may be secured to the carburetor main body by means of screws screwed into the threaded holes bored through the suction chamber and the carburetor main body but in such a manner that the relative position of the nozzle 8 and jet needle 7 may be reproducible before and after assembly and disassembly of the carburetor. To this end, in the present invention the screws are fabricated in such a shape as will provide for sliding movement to some extent of the suction chamber 2 on the contacting face 10 of the carburetor main body 1, and positioning pins 11 are provided at least at two locations, extending through the suction chamber 2 into the carburetor main body 1. The details of an example of the positioning pin 11 is shown in FIG. 2. Each of the positioning pins 11 is formed by pouring a 'molten thermosetting resin 14 from the upper side into a hole 12 bored through the movable side or the boss 2' of the suction chamber 2 and a hole 13 bored in the stationary side or the boss of the carburetor main body 1 in communication with said hole 12, prior to adjustment of the amount of eccentricy between the jet needle 7 and nozzle 8, and setting the molten resin in said holes, either with heat or at nomal temperature. In this case, it is effective to use, for example, such a thermosetting resin which is flowable at normal temperature and highly adhesive to metal surface, such as epoxy resin.

The hole 13 is communicated with the outside through a vent hole 15 extending from the side wall or bottom wall of said hole 13 so that said hole 13 may be completely filled with the resin, and the diameter A at the lowest portion of the hole 12 is made larger than the diameter B of the hole 13, to such an extent that the upper surface of the hole 13 may remain inside the lower face of the hole 12 even after said holes are offeentered due to positional adjustment of the suction chamber 2 relative to the carburetor main body 1. Namely, since the holes 13, 12 are formed beforehand in the stationary side (carburetor main body) and the movable side (boss of the suction chamber), it is natural that the holes l2, 13 are off-centered after the adjustment of the amount of eccentricity between the nozzle 8 and jet needle 7. However, even when the holes l2, 13 are off-centered, the resin pured into the hole 12 flows into the hole 13 as the diameter at the bottom of the hole 12 is larger than the diameter of the hole 13 as stated above, and forms the positioning pin ll upon setting. It is necessary to apply a thin layer of a releasing agent to the inner surface of the hole 12 in the movable side to prevent the resin from bonding to the metallic contacting face of the carburetor main body. The contacting faces of the stationary and movable sides are brought into contact with and bonded to the resin respectively, due-to relative displacement of the suction chamber and carburetor main body, and secured to each other. The bonding of the contacting faces may be avoided by applying the releasing agent also to the contacting faces, but the application of the releasing agent in too a large thickness will result in lifting of the suction chamber 2, making uniform connection of said suction chamber impossible and in a change in the angle of inclination of the suction chamber 2 when the releasing agent has been removed during disassembly of the carburetor, thus impairing the reproduction of the amount of eccentricity of the jet needle 7.

It has been confirmed that these problems can be solved without applying the releasing agent to the contacting faces of the stationary and movable sides, by making the outer diameter of the positioning pin 11 larger at the movable side than at the stationary side as stated above, and applying the releasing agent only to the inner surface of the hole in the movable side. The thickness of the releasing agent, applied to the inner surface of the hole 12 formed in the movable side, is very small as compared with that of the releasing agent applied to the contacting faces of the carburetor main body 1 and suction chamber 2 and, therefore, has little adverse affect on the accuracy of operation of the car buretor.

The diameter of the hole 12 in the movable side is progressively decreased upwardly as shown, whereby the removal of the positioning pin and re-assembly of the carburetor are facilitated. The inner surface of the hole 12 in the movable side is coated with the releasing agent prior to pouring of the resin. Then, the resin is poured into the hole 12 from the upper side. Upon hardening of the resin, the positioning pin 11 is formed in a shape complementary to the shape of the pinreceiving hole formed by the holes 12, 13, and the pinforming resin is bonded to the surface of the carburetor main body 1 at the joint 16 of the holes 12, 13 and at the inner surface of the hole 13. However, the resin is not bonded to the suction chamber 2, so that said suction chamber 2 is freely removable from the carburetor main body 1. After the jet needle 7 and nozzle 8 are positioned accurately by forming the positioning pins 11 in the manner described, the suction chamber 2 and the carburetor main body 1 are fixedly connected together by means of screws (not shown).

Where a thermoplastic resin, such as polypropylene resin, is used for the pin-forming resin, the use of the releasing agent may occasionally by unnecessary but in this case it is only necessary to fix the positioning pin to the carburetor main body by taking advantage of the vent hole 15.

According to the present invention, it is unnecessary to mechanically drive the positioning pins and accordingly a variation of fuel flow rate due to a relative positional deviation of the jet needle and nozzle, otherwise caused by vibrations or shocks given to the carburetor during driving of the positioning pins, can be prevented. In a prior art method in which nock pins are mechanically driven as positioning pins, there has occured 15 20 percent of flow rate variation, but according to this invention such flow rate variation can be completely avoided as no vibrations nor shocks are given to the carburetor during assembly of said carburetor.

Further, in the above-described prior art method the size of play of the jet needle relative to the nozzle is determined by the dimensional accuracy of the pinreceiving hole and the method of driving a positioning pin into said hole, etc. but according to the present invention it is determined only by the slight gap formed by the releasing agent, which can be made uniform by properly selecting the coating method. Therefore, the relative position of the suction chamber and the carburetor main body and hence the relative position of the jet needle and the nozzle can be reproduced after disassembly and re-assembly of the carburetor with high uniformity.

It is also to be noted that in the present invention the positioning pins can be produced in a simple operation and with high accuracy, by making use of the carburetor main body, etc., by properly selecting the shape of the pin-receiving hole.

in the method utilizing nock pins, much care must be exercised in the hole boring and pin driving operations subsequent to adjusting the amount of eccentricity between the jet needle and the nozzle, but according to the present invention any one can carry out the assembly of the carburetor main body and suction chamber in the desired relative position, with much simplicity.

The pin-forming material is not restricted only to resins but any material may be used which is capable of forming the positioning pins, owing to the characters of the pin-receiving hole described previously.

Further, the air valve-type carburetor to which the present invention is applicable may be of any construction other than that of the embodiment described and illustrated herein, provided that it has a combination of a jet needle and a nozzle.

We claim:

1. In an air valve*type carburetor comprising a main body, a suction chamber fixed to said main body, a suction piston mounted in said suction chamber and slidingly projecting from or retracting into said suction chamber according to the suction pressure in an air intake passage in the carburetor main body to vary the Ventri area in said air intake passage, a nozzle retained in the carburetor main body, and a jet needle fixed to said suction piston and extending into said nozzle, the position of said jet needle being displaced relative to said nozzle, whereby the fuel metering area of said carburetor is varied, in which the relative position of said nozzle and jet needle being determined accurately by shifting said suction chamber relative to said carburetor main body, and said suction chamber and carburetor main body being fixed in the thus determined relative position by means of positioning pins; a method of producing the positioning pins, comprising boring holes in the carburetor main body and the boss of the suction chamber, in communication with each other, to form a positioning pin-receiving hole, and pouring a pinforming material, such as a resin, into said positioning pin-receiving hole, after setting the carburetor main body and the suction chamber in the desired relative position.

2. A method of producing positioning pins, as defined in claim 1, comprising forming a nozzle guide in the carburetor main body, slidably disposing the nozzle in said nozzle guide, forming the mating surfaces of the carburetor main body and the boss of the suction chamber having the jet needle fixed thereto in such a manner that they are at right angles to the axis of said nozzle guide, boring holes through the boss of the suction chamber and in the carburetor main body respec tively in communication with each other to form a pinreceiving hole, the diameter at the mating end of the hole formed through the suction chamber boss being larger than the diameter at the opposite mating end of the hole formed in the carburetor main body, and pouring a pin-forming material, such as a resin, into said pin-receiving hole to form the positioning pin.

3. A method of producing positioning pins of an air valve-type carburetor, as defined in claim 2, wherein a thermosetting resin is poured into said pin-receiving hole from the upper side to form the positioning pin after applying a releasing agent to the inner surface of the hole formed through the movable side or the suction chamber boss.

41. A method of producing positioning pins of air valve-type carburetor, as defined in claim 2, wherein a vent hole is provided in communication with the hole bored in the stationary side or the carburetor main body.

5. A method of producing positioning pins of an air valve-type carburetor, as defined in claim 2, wherein the diameter of the hole bored through the movable side or the suction chamber boss is progressively increased toward the stationary side or the carburetor main body.

6. An air valve-type curburetor of a variable Venturi type, having a main body, a suction chamber fixed to said main body, a suction piston mounted in said suction chamber and slidingly projecting from or retracting into said suction chamber according to the suction pressure in an air intake passage in said carburetor main body to vary the Ventri area in said air intake passage, a nozzle retained in said carburetor main body and ajet needle fixed to said suction piston and extending into said nozzle, the position of said jet needle being displaced in said nozzle, whereby the fuel metering area ofsaid carburetor is varied, in which the relative position of the nozzle and jet needle is accurately determined by shifting the suction chamber relative to the carburetor main body, and said suction chamber and carburetor main body are fixed in said relative position by means of positioning pins, said carburetor being characterized in that said positioning pins are molded of a pin-forming material, such as a resin, poured into a plurality of pin-receiving holes each formed of a hole bored through the boss of the suction chamber and a hole bored in the carburetor main body in communication with said hole through the suction chamber boss, after said suction chamber and carburetor main body have been set in the desired relative position. 

1. In an air valve-type carburetor comprising a main body, a suction chamber fixed to said main body, a suction piston mounted in said suction chamber and slidingly projecting from or retracting into said suction chamber according to the suction pressure in an air intake passage in the carburetor main body to vary the Ventri area in said air intake passage, a nozzle retained in the carburetor main body, and a jet needle fixed to said suction piston and extending into said nozzle, the position of said jet needle being displaced relative to said nozzle, whereby the fuel metering area of said carburetor is varied, in which the relative position of said nozzle and jet needle being determined accurately by shifting said suction chamber relative to said carburetor main body, and said suction chamber and carburetor main body being fixed in the thus determined relative position by means of positioning pins; a method of producing the positioning pins, comprising boring holes in the carburetor main body and the boss of the suction chamber, in communication with each other, to form a positioning pin-receiving hole, and pouring a pin-forming material, such as a resin, into said positioning pin-receiving hole, after setting the carburetor main body and the suction chamber in the desired relative position.
 2. A method of producing positioning pins, as defined in claim 1, comprising forming a nozzle guide in the carburetor main body, slidably disposing the nozzle in said nozzle guide, forming the mating surfaces of the carburetor main body and the boss of the suction chamber having the jet needle fixed thereto in such a manner that they are at right angles to the axis of said nozzle guide, boring holes through the boss of the suction chamber and in the carburetor main body respectively in communication with each other to form a pin-receiving hole, the diameter at the mating end of the hole formed through the suction chamber boss being larger than the diameter at the opposite mating end of the hole formed in the carburetor main body, and pouring a pin-forming material, such as a resin, into said pin-receiving hole to form the positioning pin.
 3. A method of producing positioning pins of an air valve-type carburetor, as defined in claim 2, wherein a thermosetting resin is poured into said pin-receiving hole from the upper side to form the positioning pin after applying a releasing agent to the inner surface of the hole formed through the movable side or the suction chamber boss.
 4. A method of producing positioning pins of air valve-type carburetor, as defined in claim 2, wherein a vent hole is provided in communication with the hole bored in the stationary side or the carburetor main body.
 5. A method of producing positioning pins of an air valve-type carburetor, as defined in claim 2, wherein the diameter of the hole bored through the movable side or the suction chamber boss is progressively increased toward the stationary side or the carburetor main body.
 6. An air valve-type curburetor of a variable Venturi type, having a main body, a suction chamber fixed to said main body, a suction piston mounted in said suction chamber and slidingly projecting from or retracting into said suction chamber according to the suctiOn pressure in an air intake passage in said carburetor main body to vary the Ventri area in said air intake passage, a nozzle retained in said carburetor main body and a jet needle fixed to said suction piston and extending into said nozzle, the position of said jet needle being displaced in said nozzle, whereby the fuel metering area of said carburetor is varied, in which the relative position of the nozzle and jet needle is accurately determined by shifting the suction chamber relative to the carburetor main body, and said suction chamber and carburetor main body are fixed in said relative position by means of positioning pins, said carburetor being characterized in that said positioning pins are molded of a pin-forming material, such as a resin, poured into a plurality of pin-receiving holes each formed of a hole bored through the boss of the suction chamber and a hole bored in the carburetor main body in communication with said hole through the suction chamber boss, after said suction chamber and carburetor main body have been set in the desired relative position. 